If you ever need a prosthetic arm-and hundreds of recently wounded soldiers do-you could get a myoelectrically activated pincer sheathed in flesh-colored silicone. But eventually you might want something a bit more sophisticated. This 4-pound limb, now being developed at Vanderbilt University with a grant from Darpa, has five functioning fingers and 21 joints. Plus, it can curl 25 pounds. Oh yeah, and it's powered by a rocket. With apologies to the all-new Bionic Woman, muscles are notoriously hard to mimic with tech. Servomotors are heavy and relatively weak. Myoelectric arms, limited to just two electrodes for control, are slow and have only two joints. The rocket arm has 200 milliliters of concentrated hydrogen peroxide in an elbow-mounted cartridge. Squirt that into a nugget of iridium and the chemicals react, vaporizing the H_2O_2. The resulting 450-degree Fahrenheit gas blasts into nine cylinders, driving pistons that move the elbow, wrist, and hand (don't worry, this rig's insulated). To be fair, these limbs haven't been tried on humans yet. That won't happen until 2009, when another team of researchers completes the electrodes that will be implanted in a user's nerves to control the prosthesis. But once that's done, the rocket arm will be ready for liftoff.
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